Detection of malaria sporozoites by standard ELISA and VecTestTM dipstick assay in field-collected anopheline mosquitoes from a malaria endemic site in Ghana

We compared the VecTestTM dipstick assay for detection of Plasmodium sporozoites in Anopheles vectors of malaria with standard circumsporozoite (CS) microplate ELISA for detection of Plasmodium falciparum circumsporozoite protein (PfCSP) in Anopheles mosquitoes. Mosquitoes were collected from a malaria endemic site (Kassena Nankana district) in northern Ghana. Of 2620 randomly sampled mosquitoes tested, the standard CS-ELISA gave a sporozoite rate of 10.8% compared with 11.2% by VecTestTM, which was not statistically different (P = 0.66). Visual reading of the CS-ELISA results gave a sporozoite rate of 13.4%, which was higher than the other tests (P > 0.05). To allow a more objective evaluation of the sensitivity of the dipstick, an additional 136 known CS-ELISA-positive specimens were analysed. The prevalence of the test (including the additional samples) was 14.6% and 14.7% for CS-ELISA and dipstick, respectively (P > 0.05). The estimated prevalence by visual assessment of the CS-ELISA results was 17.5%. The relative specificity and sensitivity of the VecTestTM dipstick and visually read ELISA were estimated based on the CS-ELISA as a gold standard. The specificities of the dipstick and visual ELISA were high, 98.0% and 96.6%, respectively. However, the sensitivities of the two assays were 88.8% for VecTest and 100% for visual ELISA (P < 0.01). Concordance between VecTest and CS-ELISA was good (kappa = 0.86). Similarly, there was a good concordance between the dipstick and the visually read ELISA (kappa = 0.88). Extrapolating from PfCSP controls (titrated quantities of P. falciparum sporozoites), mean sporozoite loads of CS-ELISA-positive An. gambiae (286 +/- 28.05) and An. funestus (236 +/- 19.32) were determined (P = 0.146). The visual dipstick grades showed high correlation with sporozoite load. The more intense the dipstick colour, the higher the mean sporozoite load (+ = 108, ++ = 207, +++ = 290, r = 0.99, r2 = 1). The VecTest dipstick offers practical advantages for field workers needing rapid and accurate means of detection of sporozoites in mosquitoes.     

Interplay of oxygen-evolution kinetics and photovoltaic power curves on the construction of artificial leaves

An artificial leaf can perform direct solar-to-fuels conversion. The construction of an efficient artificial leaf or other photovoltaic (PV)-photoelectrochemical device requires that the power curve of the PV material and load curve of water splitting, composed of the catalyst Tafel behavior and cell resistances, be well-matched near the thermodynamic potential for water splitting. For such a condition, we show here that the current density-voltage characteristic of the catalyst is a key determinant of the solar-to-fuels efficiency (SFE). Oxidic Co and Ni borate (Co-B_i and Ni-B_i) thin films electrodeposited from solution yield oxygen-evolving catalysts with Tafel slopes of 52 mV/decade and 30 mV/decade, respectively. The consequence of the disparate Tafel behavior on the SFE is modeled using the idealized behavior of a triple-junction Si PV cell. For PV cells exhibiting similar solar power-conversion efficiencies, those displaying low open circuit voltages are better matched to catalysts with low Tafel slopes and high exchange current densities. In contrast, PV cells possessing high open circuit voltages are largely insensitive to the catalyst’s current density-voltage characteristics but sacrifice overall SFE because of less efficient utilization of the solar spectrum. The analysis presented herein highlights the importance of matching the electrochemical load of water-splitting to the onset of maximum current of the PV component, drawing a clear link between the kinetic profile of the water-splitting catalyst and the SFE efficiency of devices such as the artificial leaf.     

Retrospective patient dose analysis of Ghana's first direct digital radiography system

ABSTRACT: The log file generated in the flat panel detector of a direct digital x-ray machine (General Electric, Haulun Medical Systems, Serial Number 8M0392) after x-ray exposure was used to acquire data regarding the entrance surface air kerma (ESAK) for some routine x-ray examinations. The data were collected for a minimum of 10 standard adult patients undergoing each examination considered. The mean ESAK were found to be 0.25, 0.33, 0.14, 7.33, 9.76, 7.38, and 6.86 mGy for skull AP and LAT, chest AP, lumbar spine AP and LAT, pelvis AP and abdomen AP series, respectively. The mean ESAK values recorded from this study show wide variations but were below diagnostic reference levels (DRLs) of the Commission of European Communities and also compare with other recommendations. The comparisons of this study's dose levels with DRLs were undertaken as an approach to dose optimization. The study revealed that a dose audit of digital radiography systems is necessary because of the potential high doses one is likely to receive. Continuous dose evaluation in digital radiography is therefore encouraged in order to optimize doses to patients.     

Efficient solar-to-fuels production from a hybrid microbial–water-splitting catalyst system

Photovoltaic cells have considerable potential to satisfy future renewable-energy needs, but efficient and scalable methods of storing the intermittent electricity they produce are required for the large-scale implementation of solar energy. Current solar-to-fuels storage cycles based on water splitting produce hydrogen and oxygen, which are attractive fuels in principle but confront practical limitations from the current energy infrastructure that is based on liquid fuels. In this work, we report the development of a scalable, integrated bioelectrochemical system in which the bacterium Ralstonia eutropha is used to efficiently convert CO₂, along with H₂ and O₂ produced from water splitting, into biomass and fusel alcohols. Water-splitting catalysis was performed using catalysts that are made of earth-abundant metals and enable low overpotential water splitting. In this integrated setup, equivalent solar-to-biomass yields of up to 3.2% of the thermodynamic maximum exceed that of most terrestrial plants. Moreover, engineering of R. eutropha enabled production of the fusel alcohol isopropanol at up to 216 mg/L, the highest bioelectrochemical fuel yield yet reported by >300%. This work demonstrates that catalysts of biotic and abiotic origin can be interfaced to achieve challenging chemical energy-to-fuels transformations.Photovoltaics (PV) provide a scalable and cost-effective method for converting solar energy into electricity but do so only intermittently as a result of daily variations in solar intensity and the diurnal solar cycle (1–3). PV-based fuel generation can be used to bridge the gap between peak solar power and utility load curves (2, 4, 5), the simplest example of which is PV-driven water splitting to generate hydrogen as a fuel. A current lack of distribution and storage infrastructure for H₂, however, has led to slow technology adoption and thus H₂ is not yet widely used directly as a transportation fuel or for electricity generation via fuel cells (6, 7). Liquid fuels are more appealing as a solar storage medium because of their attractive energy density and existing sophisticated distribution and storage infrastructures (2). However, attempts to produce liquid fuel directly via CO₂ reduction have poor specificity and energy efficiency (8, 9) with exceptions only recently emerging (10–13).An alternative approach to the direct reduction of CO₂ to liquid solar fuels is to engineer fuel production in organisms that naturally use light energy to fix CO₂ to biomass (14–16). Notwithstanding, photosynthetic organisms suffer inefficiencies arising from nonideal light-harvesting properties that are not likely to be addressed in the near term (17). As a result, the observed solar-to-biomass efficiency by plants typically approach only 1% of the thermodynamic maximum annually (18, 19) or between 1.4% and 2.0% over the growing season when calculated on the basis of total solar radiation (17).In principle, the unique advantages of PVs and photosynthetic carbon fixation may be coupled to achieve higher solar-to-fuel efficiency (SFE), and several proof-of-principle demonstrations of this kind of coupling have been made. Electrolysis of biological culture media has been used to drive O₂ generation at the anode and, in most reports, H₂ or formate generation at the cathode (20–22). Hydrogen-oxidizing autotrophs grow on the evolved hydrogen or formate, producing biomass and, in one case, fusel alcohols (22). In other cases, the cathode may be used to deliver reducing equivalents directly to a target autotroph (23, 24) or indirectly via a soluble mediator such as Fe³⁺ or NO₂^–, which serves as the electron donor to the autotrophic microbe of interest (25, 26). In all cases, coupling these systems to a PV may enable solar-to-biomass and solar-to-fuel production (2, 27, 28).These early demonstrations of electricity-driven carbon fixation have highlighted significant impediments to the design of scalable and high SFE systems. Some promising bioelectrosynthetic systems rely on obligate anaerobic bacteria that must be kept separate from the oxygen-generating anode, making them difficult to incorporate into such an integrated system (24). For systems incorporating aerobic bacteria, a prominent impediment is the ability to implement the oxygen evolution reaction (OER) efficiently in the pH-neutral environment commonly required for biological growth. To operate in water, precious metal catalysts such as platinum or indium have been used to drive the OER. Aside from the inherent limitations imposed by the criticality of such metals (29), these metals are inferior catalysts for water splitting under biologically amenable conditions. Although the minimal thermodynamic potential required for water splitting is 1.23 V (30), previous studies have operated at total cell potentials of 4.0–5.5 V (20–22) to drive biological growth, wasting 70–80% of input energy. This inefficiency is in part due to the high overpotentials required by these metal catalysts in driving the OER.The ability to perform OER at low overpotential in neutral pH ranges (pH 6–8) has been achieved with the development of a cobalt phosphate (CoP_i) catalyst (31). This OER catalyst features many of the properties of the oxygen-evolving catalyst of photosystem II (PSII) including its structure (32–34) and its ability to self-assemble (35, 36), repair itself (37), and manage the proton-coupled electron transfer chemistry of water splitting akin to the Kok cycle of PSII (38). Of pertinence to this study, the catalyst can perform OER in natural waters of a wide variety of solution environments including buffers capable of supporting biological growth (39). When the CoP_i OER catalyst is coupled to a hydrogen evolution reaction (HER) catalyst (40), the evolved hydrogen is available for combination with CO₂, providing a foundation for the development of new biological, H₂-based CO₂ reduction strategies to produce liquid and solid fuels.In this work, a fully integrated microbial–inorganic system has been engineered based on the CoP_i water-splitting anode, with NiMoZn or stainless-steel (SS) 304 mesh 60 cathodes to generate O₂ and H₂ (41), which has in turn been used to fix carbon to biomass in wild-type (wt) Ralstonia eutropha H16 and to isopropanol in an engineered strain of R. eutropha, Re2133-pEG12. For the former, a maximal bioelectrochemical efficiency of 17.8% is achieved for biomass, and for the latter a maximal bioelectrochemical efficiency of 3.9% is achieved for isopropanol. This bioelectrochemical isopropanol fuel yield (216 mg/L) is the highest yet reported. These high efficiencies are a result of the ability to perform water splitting at lower cell voltages owing to the more efficient OER and HER catalysis.On this point, the higher voltage needed for previous bioelectrochemical cells has been identified to originate from the inability to support water splitting vs. reactive oxygen species (ROS) generation at lower potentials. When water splitting is not prevalent, current is redirected to drive parasitic reactive side reactions that generate ROS, which leads to cell death. This work lays a foundation for realizing liquid fuel production based on solar water splitting and provides an important and general proof-of-principle demonstration that inorganic and biological materials can be interfaced to achieve solar-to-fuels storage schemes that are not realized by either system in isolation. Moreover, it shows that integrated inorganic–biological hybrid systems may offer yields beyond those available to photosynthetic organisms for the production of fuels.     

Quantitative evaluation of integrated schistosomiasis control: the example of passive case finding in Ghana

Passive case finding based on adequate diagnosis and treatment of symptomatic individuals with praziquantel by the health care facilities is a minimum requirement for integrated schistosomiasis control. Two field studies were conducted in Ghana to obtain quantifications about the steps in this process: (1) a study of health-seeking behaviour through interview of individuals with reported schistosomiasis-related symptoms; (2) a study of the performance of the Ghanaian health system with regard to schistosomiasis case management by presenting clinical scenarios to health workers and collecting information about availability of praziquantel. It appeared that cases of blood in urine (the most typical symptom of Schistosoma haematobium) and blood in stool (the most typical symptom of S. mansoni) have a very small probability of receiving praziquantel (4.4% and 1.4%, respectively) from health facilities. Programmes aimed at making the drug available at all levels of the health care delivery system and encouraging health-seeking behaviour through health education are not likely to increase these probabilities beyond 30%. This is because many cases with blood in urine do not consider it serious enough to seek health care, and blood in stool usually requires (imperfect) diagnostic testing and referral. We therefore conclude that additional control activities, especially for high-risk groups, will remain necessary.